Spinel ferrite Ni0.5Zn0.3Co0.2Fe1.98O4x nanoparticles were synthesized by co-precipitation method, and samples were realized by moulding and annealing at key temperatures (TM¼800 C, 900 C, 1050 C, determined beforehand through shrinkage measurements) going with calcining and sintering processes. Annealing at 800 C and 900 C led to half-dense ceramics (porosity 50 vol. %), whereas bulky ferrite was obtained after annealing at 1050 C. Elemental analysis, X-ray diffraction and ion chromatography analysis were performed. Complex dielectric permittivity (e*) and magnetic permeability (l*) were investigated up to 6 GHz. With increasing TM, a decreasing amount of Fe2þ was observed, going with increasing sample density. Coupled effects of the Fe2þ concentration and of the porosity, both on dielectric and magnetic properties, were chiefly investigated and discussed. The materials show almost constant permittivities (e0 ¼5.0, 6.0, and 14.8 for TM¼800 C, 900 C and 1050 C, respectively). The bulk value at f¼1 GHz (e0 ¼14.8) can be interpreted well according to Shannon’s theory. The permittivities of the half-dense ceramics are discussed on the basis of Bruggeman’s Effective Medium Theory. The materials annealed at 800 degC and 900 degC show almost constant magnetic permeabilities in the frequency range from 0.2 to 1GHz (l0 ¼3.4 and 6.0 for TM¼800 degC and 900 degC). The observed permeability behavior is typical of monodomain particles, except for the sample annealed at 1050 degC, for which domain wall contribution to l* is suspected because of non-negligible losses at low frequency (l00 ¼1.3–1.8 at f<0.3 GHz). This finding is supported by estimations of the upper and lower values for the critical grain size, on the basis of Brown–Van der Zaag’s theory. Facing bulk ceramics, and in view of using Ni0.5Zn0.3Co0.2Fe1.98O4x ferrite as substrate for antenna miniaturization, the electromagnetic properties of half-dense ceramics materials seem to be very competitive at frequencies beyond 0.2 GHz, and up to 0.7–0.8 GHz.